Hot isostatic pressing (HIP) is a widely used technique for treating articles containing internal porosity to close the porosity and thus densify the article. In particular, HIP'ing is widely used in the casting industry to treat metal castings to close internal porosity and improve metallurgical structure and mechanical properties.
HIP'ing involves subjecting a casting or other article to elevated temperature and elevated gas pressure, such as argon gas pressure, for an appropriate time at temperature and pressure to achieve a metallurgical structure free of internal porosity. Equipment for conducting HIP'ing operations using high inert gas pressure is extremely expensive. Moreover, such HIP'ing equipment involves long cycle times in order to raise both temperature and pressure to the elevated levels needed as well as lower them after article consolidation is complete. As a result, although in widespread use to produce improved castings, HIP'ing adds considerably to the cost of the castings.
An alternative process that attempts to emulate HIP'ing conditions has been developed and marketed as the CERACON process to hot press metallic, intermetallic, and ceramic products. This process involves placing a preheated article in a die cavity, filling the die cavity with preheated ceramic grain or particulates, and advancing a hydraulically driven ram into the die cavity to press the particulates about the article. In this process, the particulates apply only a pseudo-isostatic pressure to the article to be densified. Moreover, this process cannot be used to treat very reactive materials, such as reactive metals (e.g. Ti and its alloys) and intermetallics (e.g. TiAl) without enclosing the article in a protective container or conducting the pressing operation in vacuum or inert gas.
There is a need for a method and apparatus for densifying articles under elevated temperature and purely isostatic elevated pressure conditions yet at lower cost than the previously used HIP process that relied on inert gas pressure.
It is an object of the invention to satisfy this need.